Growing Media Trials at the Montana
Conservation Seedling Nursery
John Justin
John Justin is Nursery Manager, Montana Department of Natural Resouces Conservation Seedling
Nursery, 2705 Spurgin Road, Missoula, MT 59804; Tel: 406.542.4327; E-mail: jjustin@state.mt.us.
Justin J. 2009. Growing media trials at the Montana Conservation Seedling Nursery. In: Dumroese,
R.K.; Riley, L.E., tech. coords. 2009. National Proceedings: Forest and Conservation Nursery Associations—2008. Proc. RMRS-P-58. Fort Collins, CO: U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station: 42–43. Online: http://www.fs.fed.us/rm/pubs/rmrs_p058.html.
Keywords: Sphagnum peat moss, vermiculite, Douglas-fir sawdust, compost
Introduction_______________________________________________________
The Montana Conservation Seedling Nursery (MCSN) in Missoula produces 750,000 container seedlings annually in
containers ranging in size from 66 cm3 (4 in3) up to 61 L (16 gal) pots. The MCSN is a production facility with no research
funding. When we encounter a promising idea for improving our seedlings or the efficiency of nursery operations, we rarely
perform detailed tests. Our standard is a “quick and dirty test.” If initial results are promising and we can eliminate anticipated risks, we quickly go operational with the change.
Growing media is one of the largest material costs in container seedling production. Frequent price increases have motivated the MCSN to evaluate numerous growing media options. Because we do not have the ability to custom mix on site,
we are limited to testing what is commercially available. For years, our standard mix consisted of 50% Sphagnum peat and
50% coarse vermiculite. This mix worked well for all our conifer production. As our species and container size options diversified, and peat and vermiculite prices increased, we began to look at other options. Our goals were to reduce growing media
costs and to find the best medium for each species we produced. We evaluated the following factors when testing growing
media:
• Cost including shipping;
• Texture and drainage;
• Wetting and drying characteristics;
• Plant response in the media; and
• Species suitable for the media.
Media Testing______________________________________________________
The MCSN evaluated the following growing media mixes over the last 6 years:
• 50% Sphagnum peat, 50% coarse vermiculite (50:50 peat:vermiculite);
• 70% Sphagnum peat, 30% coarse vermiculite (70:30 peat:vermiculite);
• 75% Sphagnum peat, 25% coarse vermiculite (75:25 peat:vermiculite);
• 70% Sphagnum peat, 30% Douglas-fir sawdust, nitroform (70:30 peat:sawdust); and
• EKO Compost™ Outdoor Planting Mix (EKO Compost; Missoula, MT).
50:50 Peat:Vermiculite Mix
Advantages, Disadvantages, Current Status—The 50:50 mix has been our standard tried and true medium, so no
surprises were found with the results. The medium wets and dries well, and is excellent for conifers and small containers.
However, the medium dries too rapidly in deciduous production, and is too light in large containers. The 50:50 peat:vermiculite
medium is excellent for growing conifers, but has become costly due to the rising cost of vermiculite and transportation costs.
Use of this mix was discontinued in 2005.
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USDA Forest Service Proceedings RMRS-P-58. 2009
Growing Media Trials at the Montana Conservation Seedling Nursery
Justin
70:30 and 75:25 Peat:Vermiculite Mixes
EKO Compost™
Advantages, Disadvantages, Current Status—Use
of either the 70:30 or 75:25 peat:vermiculite mixes would
result in a cost savings of approximately 7%. We observed
no discernable changes in plant performance. These media
wet and dry well, although they dry too rapidly in deciduous production, and are too light for large containers. The
mixes were excellent for conifers and small containers, but
both 70:30 and 75:25 peat:vermiculite mixes are costly. The
70:30 peat:vermiculite medium was used in 2005 and 2006
for all production. The 75:25 peat:vermiculite medium is
currently used for all containers under 1.6 L (100 in3), and
some conifer species in larger containers.
Advantages, Disadvantages, Current Status —EKO
Compost™ consists of composted organic matter, Sphagnum
peat moss, and pumice. The cost of this medium is approximately 50% less than all other mixes. It is available locally
and easy to order. The compost is very coarse, but holds
water well in large containers. Unfortunately, the medium
does not fill small containers well due to its coarseness, and
there is a risk of contaminants and variability in the compost
component. The large cost savings with this medium makes
it very attractive. We use this medium in all large containers over 1.6 L (100 in3) in volume, and for hardwoods grown
in 1.6 L (100 in3) containers. We have not tested the EKO
Compost™ medium in smaller containers because of concerns
with disease and drainage, especially for conifers.
70:30 Peat:Sawdust Mix
Advantages, Disadvantages, Current Status—The
70:30 peat:sawdust mix is lower in cost, will reduce excessive growth in deciduous species, but will require changes
in our fertilization program. It has caused slow growth and
stunting in many conifer species, and it dries very rapidly,
requiring an increase in irrigation frequency. We tested the
70:30 peat:sawdust medium on a small scale on numerous
species from 2002 to 2004. We found no suitable use for this
medium in our operations. Stunting and unacceptable shoot
size variation was common in all conifer species. The mix was
useful for reducing growth rates in fast-growing deciduous
plants, but the quick drying characteristics of the medium
resulted in increased irrigation costs.
Conclusions____________________
The Montana Conservation Seedling Nursery currently
uses a growing medium of 75% Sphagnum peat moss and 25%
coarse vermiculite for all seedling production in containers
smaller than 1.6 L (100 in3) in volume. We use EKO Compost™ Outdoor Planting Mix for containers with a volume of
1.6 L (100 in3) or greater, except for selected conifer species.
Growing medium with a sawdust component has not worked
in our operation, and no further testing is planned. Future
testing will focus on using 100% Sphagnum peat moss in
our small container sizes.
The content of this paper reflects the views of the authors, who are responsible for the facts and accuracy of the information presented herein.
USDA Forest Service Proceedings RMRS-P-58. 2009
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